<?php
/**
 * HeaderSelector
 * PHP version 7.4
 *
 * @category Class
 * @package  {{invokerPackage}}
 * @author   Jesse Evers
 * @link     https://highsidelabs.co
 * @email    jesse@highsidelabs.co
 */

{{>partials/partial_header}}

namespace {{invokerPackage}};

/**
 * HeaderSelector Class Doc Comment
 *
 * @category Class
 * @package  {{invokerPackage}}
 * @author   Jesse Evers
 * @link     https://highsidelabs.co
 * @email    jesse@highsidelabs.co
 */
class HeaderSelector
{
    /**
     * @param string[] $accept
     * @param string   $contentType
     * @param bool     $isMultipart
     * @return string[]
     */
    public function selectHeaders(array $accept, string $contentType, bool $isMultipart): array
    {
        $headers = [];

        $accept = $this->selectAcceptHeader($accept);
        if ($accept !== null) {
            $headers['Accept'] = $accept;
        }

        if (!$isMultipart) {
            if (is_null($contentType) || $contentType === '') {
                $contentType = 'application/json';
            }

            $headers['Content-Type'] = $contentType;
        }

        return $headers;
    }

    /**
     * Return the header 'Accept' based on an array of Accept provided.
     *
     * @param string[] $accept Array of header
     *
     * @return null|string Accept (e.g. application/json)
     */
    private function selectAcceptHeader(array $accept): ?string
    {
        # filter out empty entries
        $accept = array_filter($accept);

        if (count($accept) === 0) {
            return null;
        }

        # If there's only one Accept header, just use it
        if (count($accept) === 1) {
            return reset($accept);
        }

        # If none of the available Accept headers is of type "json", then just use all them
        $headersWithJson = preg_grep('~(?i)^(application/json|[^;/ \t]+/[^;/ \t]+[+]json)[ \t]*(;.*)?$~', $accept);
        if (count($headersWithJson) === 0) {
            return implode(',', $accept);
        }

        # If we got here, then we need add quality values (weight), as described in IETF RFC 9110, Items 12.4.2/12.5.1,
        # to give the highest priority to json-like headers - recalculating the existing ones, if needed
        return $this->getAcceptHeaderWithAdjustedWeight($accept, $headersWithJson);
    }

    /**
    * Create an Accept header string from the given "Accept" headers array, recalculating all weights
    *
    * @param string[] $accept            Array of Accept Headers
    * @param string[] $headersWithJson   Array of Accept Headers of type "json"
    *
    * @return string "Accept" Header (e.g. "application/json, text/html; q=0.9")
    */
    private function getAcceptHeaderWithAdjustedWeight(array $accept, array $headersWithJson): string
    {
        $processedHeaders = [
            'withApplicationJson' => [],
            'withJson' => [],
            'withoutJson' => [],
        ];

        foreach ($accept as $header) {

            $headerData = $this->getHeaderAndWeight($header);

            if (stripos($headerData['header'], 'application/json') === 0) {
                $processedHeaders['withApplicationJson'][] = $headerData;
            } elseif (in_array($header, $headersWithJson, true)) {
                $processedHeaders['withJson'][] = $headerData;
            } else {
                $processedHeaders['withoutJson'][] = $headerData;
            }
        }

        $acceptHeaders = [];
        $currentWeight = 1000;

        $hasMoreThan28Headers = count($accept) > 28;

        foreach($processedHeaders as $headers) {
            if (count($headers) > 0) {
                $acceptHeaders[] = $this->adjustWeight($headers, $currentWeight, $hasMoreThan28Headers);
            }
        }

        $acceptHeaders = array_merge(...$acceptHeaders);

        return implode(',', $acceptHeaders);
    }

    /**
     * Given an Accept header, returns an associative array splitting the header and its weight
     *
     * @param string $header "Accept" Header
     *
     * @return array with the header and its weight
     */
    private function getHeaderAndWeight(string $header): array
    {
        # matches headers with weight, splitting the header and the weight in $outputArray
        if (preg_match('/(.*);\s*q=(1(?:\.0+)?|0\.\d+)$/', $header, $outputArray) === 1) {
            $headerData = [
                'header' => $outputArray[1],
                'weight' => (int)($outputArray[2] * 1000),
            ];
        } else {
            $headerData = [
                'header' => trim($header),
                'weight' => 1000,
            ];
        }

        return $headerData;
    }

    /**
     * @param array[] $headers
     * @param float   $currentWeight
     * @param bool    $hasMoreThan28Headers
     * @return string[] array of adjusted "Accept" headers
     */
    private function adjustWeight(array $headers, float &$currentWeight, bool $hasMoreThan28Headers): array
    {
        usort($headers, function (array $a, array $b) {
            return $b['weight'] - $a['weight'];
        });

        $acceptHeaders = [];
        foreach ($headers as $index => $header) {
            if ($index > 0 && $headers[$index - 1]['weight'] > $header['weight']) {
                $currentWeight = $this->getNextWeight($currentWeight, $hasMoreThan28Headers);
            }

            $weight = $currentWeight;

            $acceptHeaders[] = $this->buildAcceptHeader($header['header'], $weight);
        }

        $currentWeight = $this->getNextWeight($currentWeight, $hasMoreThan28Headers);

        return $acceptHeaders;
    }

    /**
     * @param string $header
     * @param int    $weight
     * @return string
     */
    private function buildAcceptHeader(string $header, int $weight): string
    {
        if($weight === 1000) {
            return $header;
        }

        return trim($header, '; ') . ';q=' . rtrim(sprintf('%0.3f', $weight / 1000), '0');
    }

    /**
     * Calculate the next weight, based on the current one.
     *
     * If there are less than 28 "Accept" headers, the weights will be decreased by 1 on its highest significant digit, using the
     * following formula:
     *
     *    next weight = current weight - 10 ^ (floor(log(current weight - 1)))
     *
     *    ( current weight minus ( 10 raised to the power of ( floor of (log to the base 10 of ( current weight minus 1 ) ) ) ) )
     *
     * Starting from 1000, this generates the following series:
     *
     * 1000, 900, 800, 700, 600, 500, 400, 300, 200, 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1
     *
     * The resulting quality codes are closer to the average "normal" usage of them (like "q=0.9", "q=0.8" and so on), but it only works
     * if there is a maximum of 28 "Accept" headers. If we have more than that (which is extremely unlikely), then we fall back to a 1-by-1
     * decrement rule, which will result in quality codes like "q=0.999", "q=0.998" etc.
     *
     * @param int  $currentWeight varying from 1 to 1000 (will be divided by 1000 to build the quality value)
     * @param bool $hasMoreThan28Headers
     * @return int
     */
    public function getNextWeight(int $currentWeight, bool $hasMoreThan28Headers): int
    {
        if ($currentWeight <= 1) {
            return 1;
        }

        if ($hasMoreThan28Headers) {
            return $currentWeight - 1;
        }

        return $currentWeight - 10 ** floor(log10($currentWeight - 1));
    }
}
